This invention relates to protection of printed circuit (PC) structures and more particularly to an in-line printed circuit thermal fuse which is operated by heat from an adjacent component on a PC board to prevent a fire in electrical equipment. Surge arrestors such as gas tubes and carbon block protectors are required in telephone systems whenever telephone company equipment is located on or in a subscriber's premises. The are primarily used to protect a subscriber from an electrical shock which could occur from an overvoltage on the telephone lines that is caused by lightning. Since the surge arrestors protect the telephone equipment as well as the subscriber, they are also used to protect equipment such as line repeaters and subscriber terminals at other locations in the telephone system. The carbon block protector is commonly used in outside applications, e.g., where telephone wires enter a building. It consists of closely spaced carbon electrodes which discharge across an air gap at atmospheric pressure under an overvoltage. Gas tubes are also employed in such applications and are often mounted in PC boards which are made of fiberglass. Such protectors operate satisfactorily for momentary overvoltages of short duration on the telephone lines. If a high voltage power cross occurs (i.e., from a high voltage power line falling across a telephone line), however, sustained high currents in the surge arrestor may generate sufficient heat to ignite a PC board and cause an equipment fire. In order to prevent such an occurrence, a fail safe arrangement may be incorporated into the surge arrestor. A common type of fail safe arrangement comprises a lead pellet which holds a spring-loaded metal cylinder above a metal base. A sustained overvoltage on the device fires the protector continuously and heats it sufficiently to melt the lead pellet. The spring then moves the cylinder into contact with the base to permanently provide a low resistance metallic path to ground. Similar structures are combined with gas tube surge arrestors. An actuated device of such design provides a continuous short circuit across the telephone lines. Additionally, such fail safe protectors are relatively large and expensive and need not be duplicated in field equipment such as line repeaters that are mounted away from a residence on telephone poles or in a housing on a pedestal, or in the same circuit with mandatory building protection. An object of this invention is the provision of improved method and apparatus for protecting electrical equipment.